At a certain high school, 38 percent of freshmen and 31 percent of sophomores walk to school. Suppose that random samples of 40 freshmen and 45 sophomores are chosen. Let cap s is equal to the proportion of sophomores who walk to school and cap f is equal to the proportion of freshmen who walk to school. What is the probability that the proportion of sophomores who walk to school is greater than the proportion of freshmen? Use the z -table.